Mechanisms of Obesity-induced Male Infertility

Karen P Phillips; Nongnuj Tanphaichitr


Expert Rev Endocrinol Metab. 2010;5(2):229-251. 

In This Article

Reproductive Parameters in Obese Men

The relationship between semen quality and BMI has been examined in several observational studies ( Table 1 and Table 2 ). Studies set in infertility clinics have the advantage of investigating obesity trends within infertile populations whereas populations of unselected healthy men across BMI categories enable evaluation of the association between obesity and fertility without a preconceived bias. Studies designed to measure sperm parameters for obese men tended to report a negative association between semen quality and BMI ( Table 1 ).[17–21] By contrast, the large INUENDO study of European infertility patients reports no reduction in sperm concentrations or sperm motility in the obese group, whereas moderately overweight men exhibit a small decrease in sperm concentrations,[22] which is supported by more recent studies[23,24] that also report no associations between semen parameters and BMI. However, time-to-pregnancy studies support an association between subfecundity and high BMI ( Table 1 ).[25–27] Sperm concentration/total sperm count seem most likely to be negatively associated with BMI above 25 kg/m2 ( Table 2 )[17–18,20,21,28] with reduced normal sperm morphology and motility less consistent across studies ( Table 2 ).

Many population studies are limited by the small sample size of the obese study population, and tend to report overweight/obese data as a single group, which would be expected to reduce the strength of the associations measured. Possible explanations why these population studies are not more consistent could include lack of sensitivity of BMI as a measurement of adiposity, presence of subfertility, which may manifest by more subtle changes in testicular/sperm physiology not captured by traditional semen assessments, and finally, heterogeneity within the overweight/obese populations.

The association between infertility and obesity has also been examined using reproductive hormone profiles of infertility patients across BMI categories. BMI is negatively correlated with serum testosterone but positively correlated with serum estradiol in these patients;[15,22,28,29] consistent with original reports that visceral obesity in men is associated with decreased free- and total-testosterone levels[30–32] and with increased estrone and estradiol levels.[9,33–35] Therefore, it seems likely that important reproductive features of morbid obesity in men include hypogonadism, hyperestrogenemia and subfertility (Figure 5).[36]

Figure 5.

Endocrine profile of the obese male.


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